1. Field of the Invention
The present invention relates to a frequency-modulated continuous-wave (FM-CW) radar system for scanning a beam transmitted from a radar antenna, and more particularly to an FM-CW radar system which is capable of accurately detecting both the bearing and width of a target.
2. Description of the Prior Art
U.S. Pat. No. 5,369,409 discloses a time-division multiplex radar system having a plurality of antennas arranged for radiating beams having substantially the same radiation patterns in overlapping relation to each other. The beam radiated from one of the antennas is reflected by a target, and the echo signal is received by another of the antennas, such that the radar system is functionally equivalent to a radar system configuration which has a virtual antenna added between each pair of adjacent ones of the existing antennas. The disclosed time-division multiplex radar system is capable of detecting a target highly accurately in a wide angular range with the limited number of antennas.
U.S. Pat. No. 5,579,010 reveals a multibeam radar apparatus having a multibeam transmitting and receiving means, a reception level storing means for successively detecting and storing the intensities of reflected waves from targets that are received in respective transmission and reception channels and the distances up to the targets, a multibeam pattern storing means for generating and storing a multibeam pattern matrix or its inverse matrix representing the squares of directivities of the transmitted beams and corresponding to the transmission and reception channels, and an inversely processing means for arranging the stored reception levels of substantially the same distance into rows or columns corresponding to the transmission and reception channels, and processing the reception levels based of the multibeam pattern matrix or its inverse matrix to calculate corrected values of the reception levels of the transmission and reception channels. The revealed multibeam radar apparatus can detect a number of reflective sources distributed in a two-dimensional space with high resolution according to a deconvolution process.
Conventional multibeam FM-CW radar apparatus have their bearing resolution depending on the number of multiple beams. Since the number of multiple beams is limited by the structure of antennas, it is desirable to detect the bearing of a target and the width thereof in a scanning direction highly accurately without increasing the number of multiple beams.
It would be possible for beam-scanning FM-CW radar apparatus to divide a beat signal into each scanning direction and frequency-analyze the beat signal for determining the distance to and the bearing of a target. However, since the frequency-analyzing process would be time-consuming if the number of divided beat signals were increased for increased bearing resolution, it is desirable to detect the bearing of a target and the width thereof in a scanning direction highly accurately without increasing the number of divided beat signals.